Composite aluminum article



United States Patent 3,496,620 coMPostTE ALUMINUM ARTICLE Wade Wolfe, Jr., Mount Carmel, Conn., assignor to Olin Mathieson Chemical Corporation, a corporation of Virginia N0 Drawing. Filed Nov. 7, 1966, Ser. No. 592,298 Int. Cl. C22c 21/02, 21/04; B2311 3/00 U.S. 'Cl. 29-1835 7 Claims ABSTRACT OF THE DISCLOSURE The present invention relates to composite metal articles. More particularly, the present invention resides in composite metal articles having an aluminous core and an aluminous cladding, said composites having improved corrosion resistance and improved mechanical properties.

Composite aluminum articles are widely known and have been used extensively in various applications. For example, composite aluminum articles are particularly well suited for uses involving exposure to supply waters because of their lightweight and good corrosion resistance.

It is known to provide a composite having a high strength aluminum alloy core, clad with either high purity aluminum or an aluminum alloy in order to provide a more corrosion resistant coating than the core alloy itself. For example, US. Patent 1,997,165 discloses composite aluminum articles having a cladding more electronegative than the core alloy in a sodium chloride-hydrogen peroxide solution in order to provide galvanic protection to the core material. It is a finding of this patent that various alloying additions to the cladding material, such as silver, gallium, bismuth, tin, zinc, etc. will provide an alloy having a more electronegative potential in a sodium chloride-hydrogen peroxide solution than most aluminum base alloy core materials and thereby improve the corrosion resisting properties of the composite.

A typical aluminum alloy composite based on this principal uses an aluminum plus zinc alloy cladding to protect the core from corrosion. One such clad composite has a 6061 aluminum alloy core and 7072 aluminum alloy cladding (throughout the specification, aluminum alloy numbers represent Aluminum Association designations). Aluminum alloy 6061 is a heat treatable Wrought aluminum-magnesium-silicon alloy having nominal composition 1.0% magnesium, 0.6% silicon, 0.25% copper, and 0.25% chromium. Aluminum alloy 7072 has a nominal 1% zinc content in a comercial purity aluminum base. These composites do not give satisfactory service in many sections of the country. For example, the addition of zinc to aluminum decreases general corrosion resistance of aluminum in salt environments and in acidic conditions, such as industrial atmospheres. Accordingly, aluminum alloy 7072 is attacked by many atmospheres and becomes etched and disfigured by the accumulation of corrosion p oducts. In addition, aluminum alloy 7072 is not particularly strong nor abrasion resistant and thereby detracts from the strength of many cores on which it is clad and provides a surface which is easily disfigured by abrasion.

Furthermore, alloy 7072 is sufficiently electronegative so that when tiny pits penetrate to the core-clad interface, the pits rapidly broaden by galvanic corrosion of 7072 3,496,620- Patented Feb. 24, 1970 ice and soon detract from the appearance of the clad surface. The zinc content of the clad alloy also presents a scrap recovery problem.

The foregoing disadvantages are true generally with cladding materials containing greater than 0.8% Zinc. More noble core alloys, such as aluminum alloy 2024, are protected with relatively pure aluminum alloys. However, commercially available aluminum core materials containing magnesium as one of the major alloying elements are normally clad with high zinc containing alloys, such as 7072.

Accordingly, it is a principal object of the present invention to provide an improved composite alloy having an aluminous core and an aluminous cladding.

It is an additional object of the present invention to provide a composite material as aforesaid having improved corrosion resistance and improved mechanical properties.

It is an additional object of the present invention to provide an improved composite as aforesaid wherein the core material contains magnesium as one of the major alloying elements and the cladding has a low zinc content.

It is a still further object of the present invention to provide an improved composite as aforesaid which composite is strong and abrasion resistant and is not easily disfigured by abrasion.

A still further object of the present invention is to provide an improved composite as aforesaid which presents minimal scrap recovery problems.

Further objects and advantages of the present invention will appear hereinafter.

In accordance with the present invention it has now been found that the foregoing objects and advantages are readily obtained. The composite alloy of the present invention has a non-heat treatable core containing from 0.2 to 2.8% magnesium, from 0.10 to 1.5% manganese, up to 1.0% silicon, up to 0.3% copper, up to 1.0% iron, up to 0.5% zinc, up to 0.5% chromium, others 0.5% each, total 0.15% balance essentially aluminum, clad with a dissimilar alloy containing 0.5 to 3.0% magnesium, up to 0.3% zinc, up to 0.4% silicon, up to 1.0% iron, up to 0.3% copper, up to 0.2% manganese, up to 0.3% chromium, others 0.5 each, total 0.15 The cladding should preferably contain more magnesium than the core and preferably at least 0.5 more magnesium than the core. In addition, the core should preferably contain more than the cladding of one or more of the following elemen s: copper, manganese and chromium.

The cladding material represents from 1.0 to 20% of the total thickness of the composite. The cladding may be on either one or preferably both sides of the core. Where the cladding is on both sides of the core it is preferred that each cladding represent from 1.0 to 10% of the total thickness of the composite per side.

It has been found in accordance with the present invention that the foregoing composite material readily overcomes the disadvantages of the art. The addition of magnesium to the cladding material provides stronger and more abrasion resistant composites than heretofore available. Furthermore, the aluminum magnesum clad alloys of the present invention are more corrosion resistant than zinc containing claddings, such as aluminum alloy 7072. In the composites of the present invention the cladding galvanically protects the core but does not overprotect the core and waste the cladding. Hence, the cladding will have a longer life than zinc containing claddings, such as aluminum alloy 7072 and will maintain a better general appearance without unsightly broadening of pits through rapid and unnecessary galvanic corrosion of the cladding.

Furthermore, the aluminum-magnesium clad alloy of the present invention is totally acceptable for recycle, as

scrap, into production of those core alloys which also contain magnesium. Normally, composites having zinc containing aluminum alloy claddings, such as aluminum alloy 7072, suffer from the disadvantage that the zinc content of the cladding is incompatible with the production of many core alloys with which it is used.

The core material is any alloy falling within the foregoing compositional ranges. The core material contains magnesium in an amount from 0.2 to 2.8% and preferably from 0.8 to 1.1%. The core material is a non-heat treatable alloy and the cladding should preferably contain more magnesium than the core, with the cladding preferably containing greater than 0.5% magnesium than the core.

The core alloy may also contain the following ingredients in the following ranges: silicon up to 1.0%, preferably 0.15 to 0.7%, copper up to 0.3%, preferably 0.10 to 0.25%, iron up to 1.0% preferably 0.5 to 0.7%, manganese 0.1 to 1.5%, preferably 1.0 to 1.5%, zinc up to 0.5%, preferably up to 0.25%, chromium up to 0.5%, preferably 0.08 to 0.12%. In addition, it is desirable that these elements remain in solid solution in the aluminum alloy.

In addition, the core should preferably contain more than the cladding of one or more of the following elements: copper, manganese, and chromium in order to obtain a protective galvanic current between the cladding and the core alloys.

Typical core materials which may be employed include for example, aluminum 3004, 3105 and 5052.

The cladding material contains magnesium in an amount from 0.5 to 3.0%. In addition, the cladding may contain the following other materials. Zinc up to 0.3%, preferably up to 0.25 silicon up to 0.4%, preferably up to 0.2%, iron up to 1.0%, preferably up to 0.5%, copper up to 0.3%, preferably up to 0.05%, manganese up to 0.2%, preferably up to 0.10%, chromium up to 0.3%.

Typical cladding materials include the following 2.1- loys: 5050, 5252, 5005 and so forth.

The method of forming the composite of the present invention is not particularly critical and any desired method for obtaining a metallurgically bonded composite may be employed, such as conventional casting, spraying or rolling techniques. For example, the core and cladding may be rolled together at from 800 to 1000 F. followed by rolling to finish gauge without an intermediate anneal at a temperature under 600 F.

The present invention and the improvements resulting therefrom will be more readily apparent from a consideration of the following illustrative examples.

EXAMPLE I The following example describes the preparation of the typical composition of the present invention. Aluminum alloy 5050 was clad 5.8% on both sides of aluminum alloy 3004. The following steps were performed.

Step IAn ingot was cast of aluminum alloy 3004 of the size 16" x 45" x 85" and of the composition: silicon 0.22%, iron 0.62%, copper 0.14%, manganese 1.11%, magnesium 1.00%, Zinc 0.03%, others less than 0.05%, total less than 0.15%.

Step IIThe ingot was homogenized, and approximately 0.25" was scalped from each side.

Step III-A liner ingot was cast of aluminum alloy 5050 of the size 16" x 45" x 150" and of the composition: silicon 0.06%, iron 0.50%, copper 0.04%, manganese 0.02%, magnesium 1.53%, chromium 0.01%, Zinc 0.03%, other less than 0.05% each, total less than 0.15%.

Step IVThe ingot of aluminum alloy 5050 Was sclaped, heated to 800 to 850 F., hot rolled to 1.00" gauge and sheared to provide two 1.00" X 43" X 83" slabs.

Step V-One liner slab of aluminum alloy 5050 Was pla ed beneath the i g of a uminum alloy 3004. An

additional liner slab of aluminum alloy 5050, as described above, was centered and placed upon the ingot. The total composite was heated for hot rolling at a temperature in range of 700 to 750 F.

Step VIMetallurgical bonding of the 5 5 004/ 5050 composite was accomplished by hot rolling in a reversing mill which reduced the thickness to 0.702 gauge.

Step VIIWhile still. hot, the composite was further reduced in a 3-stand mill to 0.2175 gauge. The hot mill sheet was slit to a 42" width, coiled and allowed to cool to room temperature.

Step VIIIThe 505 0/ 3004/ 5050 sheet was further reduced by cold rolling in three passes to 0.050" gauge.

Step IXThe cold rolled sheet was further slit into two coils together with the appropriate removal of scrap from the edges. One coil was 25.5 Wide.

Step XThe 25 .5" wide coil was flattened and sheared to provide flat sheets each 25.5 wide x long x 0.050" gauge.

Step XI--Some of the sheets described in Step X were stabilized to the H-36 temper by a 2-hour soak at 300- 325 F.

Step XII-The above stabilized sheets were then stretcher straightened.

Step XIII-One of the sheets from Step X was annealed to the 0 temper.

EXAMPLE II The mechanical properties of the composite aluminum article, described above in Example I, are shown in the following table.

TABLE I Percent 0.2% Ofiset Ultimate, Elongation Material Temper Yield, p.s.i. p.s.i. in 2 From Step X H-16 42, 210 43, 450 2. 8 From Step XII 11-36 39, 950 41,980 5. 8 From Step XIII 0 10, 420 25, 20. 6

EXAMPLE III TABLE II Temper H-36 0.2% offset yield, p.s.i. 36,834 Ultimate p.s.i. 39,818 Percent elongation in 2" 6.3

Typical mechanical properties of clad aluminum alloy 3004 (7072/3004/7072) produced with this equipment are shown as the following average values from several lots of 0.500" gauge sheet.

TABLE III Temper H-36 0.2% offset yield, p.s.i 37,500 Ultimate p.s.i 40,000 Percent elongation in 2" 5.0

EXAMPLE IV The composite aluminum article described in steps I through XII of Example I was sheared into 4" x 6" x 0.050" gauge panels.

Three of these panels were exposed for 1000 hours to neutral salt spray. This exposure was carried out by a procedure described in ASTM Designation Bll7-57T which requires a fog of sodium chloride at 95 +2 to 3 F. It was found that the composite aluminum article 6 copper, up to 1.0% iron, from 0.10 to 1.5% manganese, up to 0.5% zinc, up to 0.5% chromium, others each 0.05%, total 0.15%, balance essentially aluminum, said core being a non-heat treatable alloy; (B) clad with a dissimilar alloy consisting essentially was significantly more resistant to this environment than 5 of from 0.5 to 3.0% magnesium, up to 0.3% zinc, up bare (unclad) aluminum alloy 3004 panels exposed durto 0.4% silicon, up to 1.0% iron, up to 0.3% coping the same test. per, up to 0.2% manganese, up to 0.3% chromium,

Three additional panels of the composite aluminum others each 0.05%, total 0.15%, balance essentially article were exposed for 392 hours to acidified salt spray. 10 aluminum;

This exposure was carried out by a procedure described (C) wherein the cladding represents from 1.0 to 20% in ASTM Designation B287-57R which requires a fog of the total thickness of the composite; and of 5+ sodium chloride solution, adjusted to a pH of 3.1 (D) wherein said core contains more than said cladto 3.3, at a temperature of 95 +2 to 3 F. During this ding of a material selected from the group consisting test it was found that aluminum alloy 5050 galvanically of copper, manganese and chromium. protected the underlying aluminum alloy 3004 core where- 2. A composite aluminous article: by pits were confined to a depth at or near the clad-core (A) having a core consisting essentially of from 0.2 interface (the cladding thickness was 0.00289 on both to 2.8% magnesium, up to 1.0% silicon, up to 0.3% sides). Considerable protection was afiorded by the alucopper, up 1.0% iron, from 0.10 to 1.5% mangaminum alloy 5050 clad compared to bare (unclad) alunese, up to 0.5% zinc, up to 0.5% chromium, others minum alloy 3004 on which the average pit depth was each 0.05%, total 0.15 balance essentially alumifound to be 9.6 mils and pits as deep as 18 mils Were num, said core being a non-heat treatable alloy; found during the same test. (B) clad with a dissimlar alloy consisting essentially of from 0.5 to 3. 0% magnesium, up to 0.3 zinc, up EXAMPLE V to 0.4% silicon, up to 1.0% iron, up to 0.3% cop- The above Example IV shows that aluminum alloy per, up to 0.2% manganese, up to 0.3% chromium, 5050 cladding will protect a core of aluminum alloy 3004 others each 0.05%, total 0.15%, balance essentially in accelerated test conditions. Galvanic protection was alu i m, id l ddin nt ining mor magnesium also found when equal areas of aluminum alloy 5050 th n said core; and aluminum alloy 3004 were immersed in a 0.1 molar (C) wherein the ladding re ese t from 1.0 to 20% sodium chloride solution at temperatures of 25 -32 C., of the total thickness of the composite; and coupled outside the solution through suitable current (D) wherein said core contains more than said cladmeasuring devices. The direction of current was such ding of a material selected from the group consisting that aluminum alloy 5050 behaved electrochemically as f r, manganese and chromium. an anode and aluminum alloy 3004 as a cathode without 3, A composite according to claim 2 wherein the core reversing direction of flow during 1.40 hours of measureis lad on both sides. n e galvanic Current Was initially h and slowly 4. A composite according to claim 2 wherein said core decreased to a steady state value within about 120 hours. tai f 0.8 t 1.1% magnesium, from 0.15 to 0.7 The total current expressed in coulombs, during 140 ili o from 010 to 0.25% copper, from 0.5 to 0.7% hours and the steady state current are shown in Table i f 1 t 15% manganese, up t 0,25% in IV as Cell Number 3. and from 0.08 to 0.12% chromium.

Table IV also shows that even higher protective cur- 5. A composite according to claim 2 wherein the cladrents can be obtained by increasing the copper content ding contains greater than 0.5% magnesium than the of the aluminum alloy 3004 cathode (Cell No. 4) or o e, increasing the chromium content (Cell No. 5). 6. A composite according to claim 2 wherein said alloy- The galvanic currents found with other aluminum alloy ing ingredients in said core are in solid solution. clad-core combinations are shown as Cell Nos. 1, 2 and 7. A composite according t claim 2 wherein said 6 in Tabe IV. cladding contains up to 0.25% zinc, up to 0.2% silicon,

TABLE IV Steady Percent State Cell No. Electrode Alloy Si Fe Cu Mn Mg Cr Zn Ti Coulo r ri ii s r iii riiz 5052 0.10 0. 2s 0. 05 0. 03 2.30 0.10 0. 03 0. 01 i 5050 0.12 0. 4s 0. 30 0. 03 1.53 0. 01 0. 02 0. 013

1 Total coulombs during 140 hours.

2 Galvanic current after 140 hours, micro-amperes per square inch.

This invention may be emboddied in other forms or up to 0.5% iron, up to 0.05% copper, and up to 0.10% carried out in other ways without departing from the manganese. spirit or essential characteristics thereof. The present en1- References Cited bodiment is therefore to be considered as in all respects illustrative and not restrictive, the scope of the invention UNITED STATES PATENTS being indicated by the appended claims, and all changes 1,805,448 5/1931 Frary 29l975 which come within the meaning and range of equivalency 1,997,166 4/1935 Brown 291975 are intended to be embraced therein. 2,726,436 12/1955 Champion 29' 197-5 What is claimed is:

1. A composite aluminous article: HYLAND BIZOT Primary Exammer (A) having a core consisting essentially of from 0.2 U.S. Cl. X.R.

to 2.8% magnesium, up to 1.0% silicon, up to 0.3% 75 29l97.5 

